FIG. 1 shows a device for transmitting data to and receiving data from a smart card 1. When being transmitted to the smart card, the data to be transmitted is applied to a modulator 4 that receives a carrier. According to the EPC Global standard, this carrier is located in the UHF band between 868 MHz and 925 MHz. The output signal of the modulator is supplied to a transmitting/receiving antenna 2 by a coupler 3. When being received, the data transmitted by the smart card 1 is received by the antenna 2 and applied by the coupler 3 to a circuit 5 for IQ demodulation, filtering and amplification that makes it possible to extract, from the signal received, the envelope of the carrier constituting the encoded data. This encoded data is applied to a decoding device 6 that delivers decoded data.
FIG. 2 shows the principle of encoding data in accordance with the EPC Class1-gen1 protocol. In this figure, a binary “0” is transmitted in the form of a square wave period with a period t0, while a binary “1” is transmitted in the form of two square wave periods with a period t0/2 in phase with the signal corresponding to the binary “0”. FIG. 8 shows the form of an encoded data CD signal according to the principle shown in FIG. 2. The example of FIG. 8 shows the signal for encoding the binary data “00110000”.
In general, the decoding of the encoded data signal that is received, which is performed by the decoding device 6, involves a microcontroller which must be controlled by a clock signal CLK that is synchronous with the encoded data signal received.